This code establishes standard procedures for conducting subsurface investigations for foundation design. It provides comprehensive guidelines on the methods of exploration, sampling techniques, groundwater monitoring, and specifies the recommended depth and spacing of boreholes based on the structure type.
Provides guidelines for planning and carrying out site investigations for foundations, including boring, sampling, and in-situ tests.
Quick Reference Values
depth of exploration isolated footing1.5 times the width (1.5B) below foundation level
depth of exploration raft foundation1.5 times the width of the raft below foundation level
depth of exploration pile group1.5 times the width of pile group below pile tip elevation
minimum boreholes compact building3 boreholes (not in a straight line)
groundwater stabilization timeMinimum 24 hours after completion of boring
Key Formulas
Significant depth of exploration = Depth where the net increase in vertical stress is less than 10% of the initial effective overburden stress
Practical Notes
Boreholes should never be arranged in a single straight line for a building; a staggered or triangular layout is required to properly establish the dip of the soil strata.
Groundwater level readings must be taken only after the water table has sufficiently stabilized, which generally requires waiting at least 24 hours after the boring operation is completed.
Exploration depth must always extend through any upper weak or highly compressible strata into a firm bearing layer, overriding the 1.5B rule of thumb if necessary.